In the machine tool industry, those of skill in the art will recognize that end mills are generally provided as cylindrically shaped cutting tools with a shank end and a cutting end having flutes (with or without helix design) that define side cutting edges which intersect with the end of the end mill, generally with a slight concave dish of from about 1 to about 3 degrees of inward dish angle (that is, from the radial edges inward toward the center of rotation). The existing end mill cutting tools of which we are aware are provided based on designs that are generally capable of plunging or pecking with multiple small axial steps, or which are capable of ramping at relatively slight angles, such as between about one-half (½) degree to about three (3) degrees. The actual degree of ramping achievable is often primarily dependent upon the machineability of the material being cut. In many such machine tool designs, exceeding such just mentioned ramping angles during machining on a workpiece causes elevated cutting forces, and possibly catastrophic failure, due to excessive tool to part contact. Such failures are, in part, due to inefficient geometry of cutting face design of such prior art tools.
To avoid such problems, various techniques have been developed, and such prior art techniques are presently widely used in machining workpieces. For example, the technique of pocketing may be utilized, wherein one first uses a drill to manufacture a hole, and then the end mill is inserted into the hole, and subsequently a slot is machined in a lateral direction. Another method, namely slotting, may be utilized, where an open end allows machining to start at an outside or exposed edge, and multiple slot cuts of shallow depth are utilized. The first approach, i.e. pocketing, requires the use of two tools—a drill and an end mill. Both techniques require multiple machining steps. Thus, both of those techniques are inefficient. Extra time is consumed during parts manufacture by the use of such processing techniques. And, in many respects, high or excessive cutting pressure may decrease tool life. Also, the cutting pressure or heat generated in such prior art techniques may decrease the quality of the part made from the workpiece being machined.
One relatively recent patent, namely U.S. Pat. No. 6,435,780, issued Aug. 20, 2002 to C. M. Flynn for a Rotary Cutting Tool has made an attempt at reducing forces encountered during end milling. However, only material listed in the published test results was 6061-T85 aluminum, which material is very easy to machine. Thus, such test results do not show the that such designs are qualified to avoid problems which are inevitably encountered when ramp machining the many and various harder or higher tensile strength materials. In the tool disclosed in that patent, an end mill having a shank end and a cutting end having flutes defining side cutting edges is provided. However, a periphery end edge portion is defined that slopes at an angle which in various embodiments may be somewhere in the range of about two (2) degrees or slightly more, and an interior edge portion is defined that slopes at an angle in the range of five (5) to twenty five (25) degrees. Thus, while such an end mill design may help to reduce the forces while ramping, such design is faced with the problem of chipping or plastic deformation of the workpiece at the working face, e.g., the outer most corner of rotation of the tool. Further, it does not provide geometry for dampening or reducing the effects of model coupling (the effect of which would be tool chatter). When ramping at angles greater than about three (3) to five (5) degrees, the result in simultaneous multi-axis machining with such a tool is that the combined directional movements form a single chip at two adjacent shear zones. These zones are located around eighty six (86) degrees from each other at the outer most tip of the cutting edges of the radial diameter, where it meets the end cutting edge forming a sharp point or tip. In the case of that tool, the chip formed is in the same shear zone at the dish end of the end mill and the outside periphery, both intersecting at the tip or corner. When those two opposing faces form a simultaneous chip at the same shear zone or chip path, they collide and compress as their directional paths intersect each other. The effect of creating two chips simultaneously in the same shear zone is more than doubling in both heat and cutting pressure at such point of intersection. When such phenomenon occurs, chips are forced and buckled as neither the shear zone near the tip or at the tip itself has a clear path for chip flow. This leads to additional strain and increased forces as the chip is then cold formed in the gullet of the flutes, resulting in additional tool pressure and heat. At this point of intersection both the heat and cutting pressure or strain is increased at the weakest point of the tool, i.e., the corner of the tool. Also, such prior art tool design does not control or allow for sufficient room for chip flow. With no specific geometry for accommodating chip formation or chip removal paths, during use, such a tool would lead to higher tool pressure at such shear zones, leading to chipping of the corner of the workpiece, or wear of the workpiece due to plastic deformation from the resulting strain and heat.
Consequently, there still remains an as yet unmet need for an end mill tool design, and a method for operation of milling machines when using such end mill tools, that takes full advantage of improved mechanical design components with respect to cutting angles and cutting speed of the improved rotary cutters disclosed and claimed herein.
Moreover, it would be advantageous to accomplish such goals while providing an rotary cutting tool suitable for use in existing milling equipment, and while providing a procedure for modification of existing parts manufacturing programs, in order to increase productivity of manufacturing operations of machined parts, and especially, those machined parts that would benefit from high speed rough end milling operations.